The present invention relates to apparatus and method for converting the information of rotation angle width into the information of time width required for a rotary machine to rotate for that rotation angle width, and is applicable effectively for example for fuel injection control system for controlling supply of fuel from a fuel injection pump to a diesel engine by means of the time control of an electromagnetic valve.
In a conventional system for controlling the supply of fuel from a fuel injection pump to a diesel engine by means of an electromagnetic valve, using a time T.sub.10 required for the fuel injection pump to rotate a unit rotation angle of 10.degree., a rotation angle width X.sub.A corresponding to a set injection quantity is converted into a time width T.sub.X by T.sub.X =T.sub.10 .multidot.X.sub.A /10, and the electromagnetic valve is time-controlled by this time width T.sub.X. However, in the conventional system, since the engine's rotation speed varies by combustion of each cylinder, there is a problem that an error occurs between the rotation angle width X.sub.A and an actual rotation angle width corresponding to the time width T.sub.X.
FIG. 1 is an explanatory drawing for explaining conversion from rotation angle width to time width in the conventional system. A waveform (A) shows the rotation speed variation of an engine, and a signal (B) shows a scale pulse train signal having a scale pulse given for each unit rotation angle of 10.degree.. The rotation angle width X.sub.A is converted to the time width T.sub.X by the above-mentioned formula by using a time T.sub.10 of a pulse spacing S.sub.10 of the scale pulse train signal. Since the rotation speed drops, the actual rotation angle width for the time width T.sub.X from a rotation angle position P.sub.X is smaller than the rotation angle width X.sub.A. Therefore, a set injection quantity corresponding to the rotation angle width X.sub.A is not given.
This problem occurs not only in the case of above-mentioned fuel injection control system but similarly in the case of converting the information of rotation angle width into the information of time width required for a rotary machine to rotate by the rotation angle width from a given set rotation angle position.